Functional analysis of piD261/Bud32, a yeast atypical protein kinase conserved during evolution

The S.cerevisiae S/T protein kinase piD261/Bud32 and its structural homologues, that are present all along the Archaea-Eukarya lineage, constitute a novel protein kinase family distantly related in sequence to the ePK superfamily. The protein plays an important cellular role as inactivation of the yeast gene encoding Bud32 results in the alteration of fundamental processes such as cell growth and sporulation. The human homologue PRPK has been shown to interact with and phosphorylate the p53 protein, notably in the regulatory Ser15 residue, thus suggesting that PRPK might play a role in the p53-mediated control of proliferative processes. Here we show that PRPK and Bud32 appear to be functional homologues, as PRPK is able to partially complement the phenotype due to the absence of the yeast protein, and that Bud32 is also able to phosphorylate the Ser15 residue of p53, a protein which is not present in yeast. Furthermore, the yeast protein Bud32 seems to be at the center of a large protein network, as demonstrated by a 2-hybrid approach and by MS analysis of immunoprecipitated Bud32: among the proteins that have been found to directly interact with Bud32, we have pointed our attention on a glutaredoxin, Grx4, and here we show the results of our studies aimed at understanding the molecular mechanism and the functional relevance of the interaction between the two proteins.